30 THE VOYAGE OF H.M.S. CHALLENGEE. 



as the type of the genus, — the Orbitolites complanata of Lamarck, which, at first known 

 only as a fossil in the Calcaire Grossier of the Paris basin and other parts of France, has 

 been since found to present itself as a li^ang form in such abundance on Australian and 

 Polynesian reefs, that its accumulated disks sometimes constitute no inconsiderable 

 proportion of their material.' The disks of this species were the earliest examples of the 

 Orbitoline type that attracted attention ; and, as I have already pointed out (pp. 1,2), 

 many strange ideas were entertained in regard to their character. When Lamarck con- 

 stituted the genus Orbitolites (p. 2), he defined this species as follows : — Orbitolites tenuis 

 fragilis, titrinque 2)lana et j^orosa; his idea having apparently been that the porosity of 

 each of its surfaces difi"erentiated it from Orbitolites marginalis, which is also utrinque 

 jjlana, but porous at the margin also. This differentiation is altogether incorrect, being 

 founded on fossil specimens whose outer lamellte have been worn away, so as to lay open 

 the subjacent chamberlets, which are closed in perfect recent specimens of Orbitolites 

 comjdanata, as in Orbitolites marginalis. The first intimation of the present existence 

 of this species seems to have been given by Defrance (Diet, des Sci. Nat., tom. xxxvi., 

 1825, pp. 294, 295), who, in describing the well-known fossil type, states that living 

 specimens closely allied to it had been found on the coast of Australia. These were pro- 

 bably the disks collected by MM. Quoy and Gaimard in that locality during the " Voyage 

 de I'Astrolabe," which they designated by the generic term Marginopora ; and this desig- 

 nation was adopted by M de Blainville (Man. d'Actinologie, 1834, p. 412), who was the 

 first to publish a description of the recent type, under the name Marginopora vertebralis, 

 in immediate sequence to that of the recent Orbitolites marginalis already cited (p. 21). 

 As in the previous case, Blainville's account of it was not only incomplete, but in some 

 respects inapplicable to the ordinary form of the type ; so that I should not have felt 

 sure of its identity, if I had not myself examined (in the Paris Museum) the very 

 specimens for which the genus Marginopora was created, and which are exactly con- 

 formable to one of the varieties of the recent Orbitolites complanata which I am about to 

 describe. The closeness of the relationship borne by his Marginojwra vertebralis to 

 Orbitolites complanata was held by Blainville to be further indicated by the conformity 

 of the internal structure of the two disks ; each being found, when one of its surfaces is 

 rubbed away, to present a series of concentric canals, separated by annular partitions, and 

 themselves divided into cells. He doubted, however, whether either Orbitolites or 

 Marginopora should be considered as a true polypary, allied to Eschara or Retep>ora ; 

 and thought it more likely that the OrbitoHne disk is " quelque piece interieure." I have 

 already alluded to the extraordinary error committed by Prof. Ehrenberg, in not only 

 .rankino- Orbitolites among his Bryozoa, in close proximity to Lunulites, but in actually 



1 I was informed by the late Prof. J. Beete Jukes, -n-hose specimens were the first which I had the opportunity of 

 examining, that at certain spots on the Australian coast the great mass of his dredgings consisted of the entire disks and 

 fragments of Orhitolites complanata, with fragments of Corallines (chiefly, I helieve, the Corallina pabnata of Ellis). 



